This invention relates to acoustic vibrating elements such as the diaphragms in loudspeakers or microphones and the cantilevers in phonographic pick-up cartridges, and to a method of manufacturing such elements from carbon.
Heretofore, aluminum and titanium have been commonly employed as materials for manufacturing electro-acoustic transducers of this type. Although these materials have a high workability factor and low densities .rho., 2.69 and 4.54 for aluminum and titanium, respectively, since they do not have a very high Young's modulus E it is difficult to manufacture high performance diaphragms from them.
On the other hand, beryllium and boron have a high Young's modulus E and low densities .rho., and thus have a high relative modulus of elasticity E/.rho.. These materials have thus been commonly employed to produce high performance diaphragms. As beryllium is poisonous, however, there are considerable environmental risks during manufacture, and the necessary equipment and safeguards for preventing such risks are quite expensive. Beryllium also has poor workability, whereby vibrating elements made thereof are very costly. Boron, on the other hand, is relatively brittle and thus low in mechanical strength, and has a low workability factor. Furthermore, it is difficult to obtain high purity boron. Accordingly, as in the case of beryllium, the cost of manufacturing boron vibrating elements is relatively high.